Renewable energy

Renewable energy refers to energy obtained from virtually inexhaustible natural sources, either because of the immense amount of energy they contain, or because they are capable of being regenerated by natural means for moderation of the mining extraction of fluids, gases and fossils.

Renewable energy includes wind, geothermal, hydroelectric, tidal, solar, wave, biomass, and biofuels. Green energy is increasingly important in today's society.

Renewable energy

Energy is obtained through wind turbines that take advantage of the kinetic energy of the wind, transforming it into electrical energy. This resource can be classified as perpetual, and the amount potentially obtainable in a specific geographical area depends on the wind regime and the orography of the place.

Wind energy, solar energy and biomass are three renewable sources of energy.

Photovoltaic solar energy installation on the roof of a rural house in Germany.

A similar, but not identical, concept is that of renewable energy: an alternative energy, or more precisely an alternative energy source is one that can replace conventional energy or energy sources, either because of its lesser polluting effect, or fundamentally because of its possibility of renewal.

Energy consumption is one of the great indicators of the progress and well-being of a society. The concept of energy crisis appears when the energy sources from which society supplies itself run out or become drastically more expensive. An economic model like the current one, whose operation depends on continuous growth, also requires an equally growing demand for energy. Since fossil and nuclear energy sources are finite, it is inevitable that at a certain moment the demand cannot be supplied and the whole system collapses, unless other new methods of obtaining energy are discovered and developed: these would be alternative energies.

On the other hand, the use of current energy sources such as oil, natural gas or coal brings with it problems such as progressive pollution, or the increase in greenhouse gases.

The alternative/conventional energy discussion is not a mere classification of energy sources, but represents a change that will necessarily have to take place during this century.

The concept «alternative energy» was born around the 70s of the last century, when the possibility began to be taken into account that the energies traditionally used, energies of fossil origin, were exhausted in a more or less short term (especially an idea extended after the publication, in 1972, of the report to the Club of Rome, The limits of growth) and it was necessary to find more lasting alternatives. Currently, it can no longer be said that they are an alternative possibility: they are a reality and the use of these energies, almost chimerical at that time, spreads throughout the world and forms part of the normal means of generating energy.

Alternative energy is a synonym for clean energy, green energy or renewable energy. Alternatives are considered to be all those that come from natural resources and inexhaustible sources, all those that, when produced, do not contaminate.

Even so, it is important to note that alternative energies, even being renewable, are limited and, like any other natural resource, they have a maximum exploitation potential, which does not mean that they can be exhausted. Therefore, even if a transition to these new energies can be made smoothly and gradually, they will not allow the current economic model based on perpetual growth to continue either. For this reason, the concept of sustainable development has emerged. This model is based on the following premises:

• The use of renewable energy sources, as fossil sources currently exploited will end up depleting, according to current forecasts, over the course of this twenty-first century.
• The use of clean sources, abandoning conventional combustion processes and nuclear fission.
• Extensive exploitation of energy sources, proposing as an alternative the promotion of self-consumption, which avoids to the extent possible the construction of large power generation and distribution infrastructures.
• Reduced energy demand by improving the performance of electrical devices (appliances, lamps, etc.).
• Reduce or eliminate unnecessary energy consumption. It is not just about consuming more efficiently, it is about consuming less, that is, developing a consciousness and a culture of energy saving and condemning waste.

Classification

Renewable sources of energy can be divided into two categories: non-polluting or clean and polluting. Among the first:

• The arrival of freshwater masses to saltwater masses: blue energy.
• Wind: wind energy.
• The heat of the Earth: geothermal energy.
• Rivers and freshwater currents: hydraulic or hydroelectric power.
• The seas and oceans: dizzi energy.
• The sun: solar energy.
• The waves: undimotriz energy.

Contaminants are obtained from organic matter or biomass, and can be used directly as fuel (wood or other solid vegetable matter), either converted into bioethanol or biogas through organic fermentation processes or into biodiesel, through reactions of transesterification and urban waste.

Energies from polluting renewable sources have the same problem as energy produced by fossil fuels: when burned they emit carbon dioxide, a greenhouse gas, and are often even more polluting since the combustion is not as clean, emitting soot and other solid particles. They are framed within renewable energies because as long as the vegetables that produce them can be grown, they will not run out. They are also considered cleaner than their fossil equivalents, because theoretically the carbon dioxide emitted in combustion has previously been absorbed by transforming it into organic matter through photosynthesis. In reality, the amount previously absorbed is not equivalent to that emitted in combustion, because in the sowing, harvesting, treatment and transformation processes, energy is also consumed, with its corresponding emissions.

In addition, much of the CO₂ emissions can be trapped to feed microalgae cultures/certain bacteria and yeasts (potential source of fertilizers and feed, salt (in the case of microalgae from brackish or salt water) and biodiesel/ethanol respectively, and means for the elimination of hydrocarbons and dioxins in the case of bacteria and yeasts (petroleum proteins) and the problem of particles is solved with gasification and complete combustion (combustion at very high temperatures, in an atmosphere very rich in O2) in combination with decontaminating means of emissions such as filters and particle precipitators (such as the Cottrel precipitator), or as activated carbon surfaces.

Energy can also be obtained from solid urban waste and from the sludge from water purification and purification plants. Energy that is also polluting, but would also be to a great extent if it were not used, since the processes of rotting organic matter are carried out with the emission of natural gas and carbon dioxide.

Historical evolution

Renewable energies have constituted an important part of the energy used by humans since ancient times, especially solar, wind and hydraulic. Sailing, wind or water mills and the constructive arrangements of buildings to take advantage of sunlight are good examples of this.

With the invention of the steam engine by James Watt, these forms of use are being abandoned, as they are considered unstable over time and capricious, and thermal and electric motors are increasingly used, at a time when the relatively low consumption, did not predict a depletion of sources, or other environmental problems that arose later.

In the 1970s, renewable energies were considered an alternative to traditional energies, both for their guaranteed present and future availability (unlike fossil fuels, which take thousands of years to form) and for their lower environmental impact. in the case of clean energies, and for this reason they were called alternative energies. Currently many of these energies are a reality, not an alternative, so the name alternatives should no longer be used.

Energy sources

Energy sources can be divided into two large subgroups: permanent (renewable) and temporary (non-renewable).

Non-renewable

Non-renewable energy sources are those that are found in nature in limited quantities. They do not regenerate or regenerate extremely slowly.

Fossil fuels are non-renewable resources, whose reserves are limited and are depleted with use. At some point they will end, and it will take millions of years to have them again. The main ones are fossil fuels (oil, natural gas and coal) and, to a certain extent, nuclear energy.

El Sharara oil field, operated by Repsol, in Libya.

Fossil energy

Fossil fuels can be used in solid (coal), liquid (oil), or gas (natural gas) forms. They are accumulations of living beings that lived millions of years ago and that have become fossilized, forming coal or hydrocarbons. In the case of coal, it is forests in swampy areas, and in the case of oil and natural gas, large masses of marine plankton accumulated on the seabed. In both cases, the organic matter partially decomposed due to lack of oxygen and the action of temperature, pressure, and certain bacteria, so that molecules with high-energy bonds were stored.

The most used energy in the world is fossil energy. Considering all that is at stake, it is extremely important to accurately measure the planet's fossil fuel reserves. A distinction is made between "identified reserves" even though they are not exploited, and "probable reserves", which could be discovered with future technologies. According to calculations, the planet can supply energy for another 40 years (if only oil is used) and more than 200 (if coal continues to be used). There are alternatives currently under study: nuclear fusion energy —non-renewable, but with immense fuel reserves—, renewable energies or hydrogen cells.

Nuclear Power

The atomic nucleus of heavy elements such as uranium can be disintegrated (nuclear fission) and release radiant and kinetic energy. Thermonuclear power plants take advantage of this energy to produce electricity through steam turbines. You get "breaking" (fissuring) atoms of radioactive minerals in chain reactions that occur inside a nuclear reactor.

A consequence of the production activity of this type of energy is nuclear waste, which can take thousands of years to disappear, because it takes that long to lose radioactivity. Currently, many countries are experimenting with fast neutron generation IV reactor models and Russia has an important model, the BN-800, operating with fuel recycled from other reactors (MOX). This allows to give more lives to the used fuel through an industrial process. Another capacity of these reactors is the reduction of waste, since they have the capacity to transmute transuranics, elements produced with the fission or breakage of the uranium nucleus and that are highly radioactive or have long half-lives, the transmutation of transuranics converts them into other chemical elements that are less radioactive or with a short half-life of minutes, days or weeks to later end up being stable elements in many cases or have much lower levels of radioactivity.

There is another possibility of nuclear energy that, so far, is only in the research phase: nuclear fusion energy, which consists of joining (melting) two hydrogen atoms to obtain one helium atom, with abundant energy production, most experts rule out that this energy source will be available to overcome global warming or for the energy transition. In this case, the fuel is hydrogen, which is abundant on earth, and the residue is helium, which is neither radioactive nor polluting. If a process is achieved to obtain this energy, it would also be non-polluting energy.

Currently, some countries prioritize the use of nuclear energy for large productions of electrical energy, as in the case of France. Humanity faces great dilemmas about the generation, distribution and use of rational energy. In this sense, the socio-controversial problem about the use of nuclear energy in the face of the energy crisis of industrialized societies remains open.

Renewable or green

Green energy is a term that describes energy generated from environmentally friendly primary energy sources. Green energies are renewable energies that do not pollute, that is, the way they are obtained or used does not emit by-products that could have a negative impact on the environment.

Currently, they are gaining more importance due to the worsening of the greenhouse effect and the consequent global warming, accompanied by a greater international awareness regarding said problem. Likewise, national economies that do not have or have exhausted their traditional energy sources (such as oil or gas) and need to acquire these resources from other economies, seek to avoid said energy dependence, as well as the negative in their trade balance that this acquisition represents.

Hydropower

The potential energy accumulated in the waterfalls can be transformed into electrical energy. Hydroelectric plants take advantage of the energy from rivers to put into operation turbines that move electrical generators. In Spain, this energy is used to produce around 15% of total electricity.

One of the most important resources quantitatively in the structure of renewable energies is that coming from hydroelectric facilities; a clean and autochthonous energy source but for which it is necessary to build the necessary infrastructures that allow to take advantage of the available potential with zero fuel cost. The problem with this type of energy is that it depends on weather conditions.

Solar thermal energy

It is about collecting the sun's energy through solar panels and converting it into heat which can be used to satisfy numerous needs. For example, hot water can be obtained for domestic or industrial consumption, or to heat homes, hotels, schools or factories. Also, refrigeration can be achieved during warm times. In agriculture, other types of applications can be achieved, such as solar greenhouses that favor crop improvements in quality and quantity, agricultural dryers that consume much less energy if combined with a solar system, and water purification or desalination plants without consuming no kind of fuel. With this type of energy, more than 25% of conventional energy consumption in newly built homes could be reduced with the consequent reduction in the burning of fossil fuels and environmental deterioration. Obtaining hot water accounts for around 28% of energy consumption in homes and these, in turn, demand a little more than 12% of the energy in Spain.^{[citation required]}

Biomass Cycle.

Biomass

Life from solar energy is carried out by the process called plant photosynthesis, which in turn triggers the biological chain. Through photosynthesis, plants that contain chlorophyll transform carbon dioxide and water from mineral products without energy value into organic materials with high energy content and in turn serve as food for other living beings. The biomass through these processes stores short-term solar energy in the form of carbon. The energy stored in the photosynthetic process can be later transformed into thermal, electrical or fuel energy of vegetable origin, releasing once again the stored carbon dioxide.

Solar Energy

Solar energy

Solar energy is a source of life and origin of most other forms of energy on Earth. Each year solar radiation provides the Earth with energy equivalent to several thousand times the amount of energy it consumes The humanity. By properly collecting solar radiation, it can be transformed into other forms of energy such as thermal energy or electrical energy using solar panels.

Using solar collectors, solar energy can be transformed into thermal energy, and using photovoltaic panels, light energy can be transformed into electrical energy. Both processes have nothing to do with each other in terms of their technology. Likewise, in solar thermal power plants, the thermal energy from solar collectors is used to generate electricity.

There are two components in solar radiation: direct radiation and diffuse radiation. Direct radiation is that which comes directly from the solar focus, without intermediate reflections or refractions. The diffuse is the one emitted by the diurnal celestial vault thanks to the multiple phenomena of solar reflection and refraction in the atmosphere, in the clouds, and the rest of the atmospheric and terrestrial elements. Direct radiation can be reflected and concentrated for use, whereas diffuse radiation coming from all directions cannot be concentrated. However, both direct radiation and diffuse radiation are usable.

You can differentiate between active and passive receptors in that the former use mechanisms to orient the receptor system towards the Sun -called trackers- and better capture direct radiation.

An important advantage of solar energy is that it allows the generation of energy in the same place of consumption through architectural integration in buildings. Thus, we can give rise to distributed generation systems in which transport-related losses -which currently account for approximately 40% of the total- and energy dependence are almost completely eliminated.

The different photovoltaic technologies are adapted to get the most out of the energy we receive from the sun. In this way, for example, photovoltaic solar concentration systems (CPV) use direct radiation with active receptors to maximize energy production and thus achieve a lower cost per kWh produced. This technology is very efficient for places with high solar radiation, but currently cannot compete in price in locations with low solar radiation such as Central Europe, where technologies such as thin film solar cells (also called Thin Film) are also managing to reduce the price of traditional photovoltaic technology to levels never seen before.

Wind power

Sunset in a wind farm located in the northeast of Germany.

Wind energy is the energy obtained from the force of the wind, that is, by using the kinetic energy generated by air currents. It is obtained by means of wind turbines that convert the kinetic energy of the wind into electrical energy by means of blades or propellers that rotate a central axis connected, through a series of gears (the transmission) to an electric generator.

The term aeolian comes from the Latin Aeolicus (ancient Greek Αἴολος / Aiolos), belonging to or relative to Aeolus or Aeolus, god of the winds in Greek mythology and, therefore, pertaining or relative to the wind. Wind energy has been harnessed since ancient times to move sail-powered ships or run mill machinery by moving their blades. It is a kind of green energy.

Wind energy is related to the movement of air masses that move from areas of high atmospheric pressure to adjacent areas of low pressure, with proportional speeds (pressure gradient). So it can be said that wind energy is a non-direct form of solar energy. The different temperatures and pressures in the atmosphere, caused by the absorption of solar radiation, are what set the wind in motion.

It is clean energy and also one of the least expensive to produce, which explains the strong enthusiasm for its applications. Among all of them, the most widespread, and the one with the greatest growth, is that of wind farms for electricity production.

A wind farm is the integrated installation of a set of electrically interconnected wind turbines. Wind turbines are the key elements in the installation of wind farms, which are basically an evolution of traditional windmills. As such, they are rotating machines that usually have three blades, about 20-25 meters long, attached to an axis. The collection element or rotor that is attached to this axis captures the energy of the wind. The movement of the blades or blades, powered by the wind, activates an electrical generator that converts the mechanical energy of rotation into electrical energy.

These wind turbines usually measure about 40-50 meters high depending on the orography of the place, but they can be even higher. This is one of the great problems that affects populations from an aesthetic point of view.

Wind turbines can work alone or in wind farms, on land forming wind farms, on the sea coast or can even be installed on the water at a certain distance from the coast in what is called offshore wind farm, which It is generating major conflicts on all those coasts where wind farms are intended to be built.

Traditional use of wind energy to remove water from a well

The great environmental benefit provided by the use of the wind for the generation of electrical energy is given, in the first place, by the levels of gaseous emissions avoided, in comparison with those produced in thermal power plants. In short, it contributes to the climate stability of the planet. A significant development of electrical energy from wind power can therefore be one of the most effective measures to avoid the greenhouse effect since, worldwide, it is considered that the electricity sector is responsible for 29% of CO emissions. ₂ of the planet.

As clean energy, it contributes to minimizing global warming. Focusing on the social and economic advantages that concern us in a much more direct way, they are greater than the benefits provided by conventional energies. The development of this type of energy can strengthen the general competitiveness of the industry and have positive and tangible effects on regional development, economic and social cohesion and employment.

There are those who ^[who?] consider that wind power is not an alternative to current energy sources, since it does not constantly generate energy when the wind is not blowing. Intermittency is one of its main drawbacks. The detrimental impact on the quality of the landscape, the effects on birds and noise, are usually the negative effects that are generally cited as environmental drawbacks of wind farms^{[citation required]}.

Regarding the effects on birds, the impact of wind turbines is not as important as it might seem at first.^{[citation needed]} Another major The drawbacks are the screen effect that significantly limits the visibility and control possibilities that constitute the raison d'être of their respective locations, a consequence of the alignment of the wind turbines. Added to the visual limitations are the foreseeable electromagnetic interference in communication systems^{[citation required]}.

Geothermal energy sources.

Geothermal energy

Geothermal energy is that energy that can be obtained by humans by taking advantage of the heat inside the Earth.

Part of the internal heat of the Earth (5,000 °C) reaches the earth's crust^{[citation needed]}. In some areas of the planet^[where?], near the surface, groundwater can reach boiling temperatures and, therefore, serve to drive electric turbines or for warm up.

The heat of the Earth's interior is due to several factors, among which the geothermal gradient and radiogenic heat stand out. Geothermal comes from the Greek geo, "Earth"; and from thermos, "heat"; literally heat of the Earth.

Tidal energy

Old tidal mill in Isla Cristina (Huelva).

Marine energy or energy from the seas (also sometimes called energy from the oceans or ocean energy) refers to renewable energy produced by ocean waves, tides, salinity and ocean temperature differences. The movement of water in the world's oceans creates a vast store of kinetic energy, or energy in motion. This energy can be harnessed to generate electricity to power homes, transportation, and industry. The main types are:

• Energy of the waves, olamotri or undimotriz.
• Energy of tides or dizziness energy.
• Energy of currents: it is the use of the kinetic energy contained in marine currents. The catchment process is based on kinetic energy converters similar to turbines using submarine water current facilities.
• Maremothermic: it is based on the use of the thermal energy of the sea based on the difference of temperatures between the surface of the sea and the deep waters. The use of this type of energy requires the thermal gradient to be at least 20. The maremothermal plants transform thermal energy into electrical energy using the thermodynamic cycle called “Rakine cycle” to produce electric energy whose hot focus is the water of the surface of the sea and the cold focus the water of the depths.
• Osmotic energy: is the energy of salinity gradients.

Green Hydrogen

The production of green hydrogen is an innovative technology that can help decarbonise the energy sector and is a promising alternative to fossil fuels, which can accelerate the energy transition in the fight against global warming^{[citation required]}.

Although hydrogen can be produced in many ways, the most exciting and promising technology is the production of hydrogen through the electrolysis of water. In this process, electrolysis breaks down water into hydrogen and oxygen through the use of electricity. If the electricity used comes from renewable energy sources such as wind energy or solar energy, then the entire energy process would be done without generating any pollution. In this case, we would be talking about “green hydrogen”, a clean energy^{[citation needed]}.

The largest green hydrogen plant for industrial use in Europe has been in Puertollano since 2022 and will serve to reduce the consumption of natural gas.

Advantages

What are the advantages of using green hydrogen as part of the energy sector?

• Hydrogen is the most abundant chemical element of nature.
• It is a universal, light and very reactive fuel.
• Reduces CO2 emissions.
• It occurs from renewable sources of energy.
• It is characterized by high energy density. A kilogram of hydrogen contains twice as much energy as one of natural gas or other fossil fuels.
• It is transportable in different states: liquid or gaseous.
• It is versatile and can be used innovatively.

Disadvantages

However, green hydrogen also has its own disadvantages, such as:

• Hydrogen is volatile. It's a flammable substance, which makes it a dangerous fuel to work.
• Electrolysis is an expensive process.
• Hydrogen is a much lighter gas than gasoline, making it difficult to store.

Possible applications

Decarbonizing residential heating systems is a major challenge in countries currently dependent on natural gas. An immediate response to the problem is to introduce green hydrogen into the process to reduce the carbon content.

In addition, in the automotive sector, green hydrogen offers an alternative to the fuels currently used and is proposed as a possible interesting solution for our future. Hydrogen vehicles complement electric vehicles to achieve a decarbonization of transportation segments.

Controversies

There is some controversy about the inclusion of incineration (within biomass energy) and hydraulic energy (on a large scale) as green energies, due to the negative environmental impacts they produce, even though they are renewable energies.

The status of nuclear power as "clean energy" is under debate. Indeed, although it presents one of the lowest rates of greenhouse gas emissions, it generates nuclear waste whose disposal is still unresolved. Under the current definition of "waste" it is not clean energy.

Although the advantages of renewable energy are notorious, they have also caused controversy in public opinion. On the one hand, environmental groups such as Greenpeace have raised their voices about the environmental impact that biomass can cause in the environment and also about the business that many have seen in this new sector. This group, together with other environmental associations, have rejected the impact that energies such as wind power have on the environment, although it is less than non-renewable sources. For this they have proposed that the generators be installed in the sea, thus obtaining a greater amount of energy and avoiding landscape pollution. However, these alternatives have been rejected by other sectors, mainly the business sector, due to their high economic cost and also, according to ecologists, due to the monopoly desire of energy companies. Some businessmen^[who?], on the other hand, defend the need for such an impact, since in this way the costs are lower and therefore the price to be paid by the users it's lower.

Environmental impact

All energy sources have some degree of environmental impact. Geothermal energy can be very damaging if heavy metals and greenhouse gases are drawn to the surface; the wind produces a visual impact on the landscape, low frequency noise, it can be a bird trap. The less aggressive hydraulics are mini-hydraulics, since large dams cause loss of biodiversity, generate methane from non-removed plant matter, cause pandemics such as yellow fever, dengue fever, schistosomiasis, particularly in temperate and hot climates, flood areas with cultural heritage or landscape, generate the movement of entire populations, among others Aswan, Itaipu, Yacyretá and increase the salinity of riverbeds. Solar energy is among the least aggressive due to the possibility of its distributed generation, except for photovoltaic and thermoelectric electricity produced in large grid-connected plants, which generally use a large area of land. The tidal power plant has been discontinued due to the very high initial costs and the environmental impact they entail. The energy of the waves together with the energy of the marine currents usually have a low environmental impact since they are usually located on rugged coasts. Biomass energy produces pollution during combustion by emitting CO2 but it is reabsorbed by the growth of cultivated plants and needs arable land for its development, decreasing the amount of arable land available for human consumption and for livestock, with the danger of increasing the cost of food and favoring monocultures.

Advantages and disadvantages of renewable energy

Ecological energies

Renewable energy sources are different from fossil fuels or nuclear power plants because of their diversity and abundance. It is considered that the Sun will supply these sources of energy (solar radiation, wind, rain, etc.) during the next four billion years. The first advantage of a certain number of renewable energy sources is that they do not produce greenhouse gases or other emissions, contrary to what happens with fuels, whether fossil or renewable. Some renewable sources^{[which one?]} do not emit additional carbon dioxide, other than what is necessary for their construction and operation, and do not present any additional risks, such as nuclear risk.

However, some renewable energy systems create particular ecological problems^{[which one?]}. Thus, the first wind turbines were dangerous for birds, since their blades rotated very quickly, while hydroelectric power plants can create obstacles to the emigration of certain fish, a serious problem in many rivers of the world (in those of the northwest of North America that flow into the Pacific Ocean, the salmon population was drastically reduced)^{[citation needed]}.

Diffuse nature

Photovoltaic solar plant operated by TEPCO in Japan.

An inherent problem with renewables is their diffuse nature, with the exception of geothermal energy which, however, is only accessible where the Earth's crust is thin, such as hot springs and geysers.

Since certain renewable energy sources provide energy of relatively low intensity, distributed over large areas, new types of "power plants" to convert them into usable fonts. For 1,000 kWh of electricity, annual per capita consumption in Western countries, the owner of a home located in a cloudy area of Europe must install eight square meters of photovoltaic panels (assuming an average energy yield of 12.5%).

However, with four square meters of solar thermal collector, a home can obtain much of the energy needed for sanitary hot water although, due to the use of simultaneity, apartment buildings can achieve the same performance with less collector surface and, what is more important, with much less investment per home.

Irregularity

The supply of electrical energy requires producing as much electricity as the network demands. But wind and photovoltaic energy are irregular: they depend on whether the wind is blowing or the sun is shining, and that moment may not coincide with the demand from the network. They therefore need means of energy storage, such as reversible hydroelectric power plants, batteries or fuel cells. Thus, energy storage costs must be taken into account when designing a self-contained renewable energy system independent of electricity. general electrical network.

On the other hand, while it is true that wind power and photovoltaics are irregular, that irregularity is highly predictable (with more than 95% reliability). This allows you to know in advance at what times of the next day you may not have enough sun or wind to meet the electricity demand, and have other sources of supply ready for that moment, such as combined cycle natural gas plants.

Polluting renewable sources

As far as biomass is concerned, it is true that it actively stores carbon from carbon dioxide, forming its mass out of it and grows while releasing oxygen again, when burned it recombines carbon with oxygen, forming again carbon dioxide. Theoretically, the closed cycle would yield a zero balance of carbon dioxide emissions, as the emissions resulting from combustion remain fixed in the new biomass. In practice, polluting energy is used in planting, harvesting and processing, so the balance is negative.

On the other hand, also biomass is not really inexhaustible, even though it is renewable. Its use can only be done in limited cases. There are doubts about the capacity of agriculture to provide the necessary amounts of plant mass if this source becomes popular, which is being demonstrated with the increase in cereal prices due to its use for the production of biofuels. On the other hand, all biofuels produce more carbon dioxide per unit of energy produced than their fossil equivalents.

Geothermal energy is not only very geographically restricted, but some of its sources are considered polluting. This is due to the fact that the extraction of underground water at high temperatures generates the dragging of unwanted and toxic salts and minerals to the surface. The main geothermal plant is located in Tuscany, near the city of Pisa and is called the Larderello Geothermal Power Plant [1] Archived 2008-08-21 at the Wayback Machine [2]. An image of the plant in the central part of a valley and the vision of kilometers of pipes one meter in diameter that go to the thermal plant show the landscape impact it generates.

In Argentina, the main power plant was built in the town of Copahue [3] and electricity generation is currently out of operation. The spring is used for district heating, street and sidewalk heating, and thermal baths.

Geographic diversity

The geographic diversity of resources is also significant. Some countries and regions have significantly better resources than others, particularly in the renewable energy sector. Some countries have significant resources close to major housing centers where electricity demand is high. The use of such resources on a large scale, however, requires considerable investment in transformation and distribution networks, as well as in production itself.

Management of electrical networks

If the production of electrical energy from renewable sources became general, the distribution and transformation systems would no longer be the large distributors of electrical energy, but would work to locally balance the electricity needs of small communities. Those who have surplus energy would sell to deficit sectors, that is, the exploitation of the network should go from "passive management" where some generators are connected and the system is boosted to obtain the "downstream" towards the consumer, to an "active" management, where some generators are distributed in the network, having to constantly monitor the inputs and outputs to guarantee the local balance of the system. That would require major changes in the way networks are managed.

However, the small-scale use of renewable energy, which can often be produced "on-site," decreases the need for electricity distribution systems. Typical systems, rarely economically profitable, revealed that an average home with a solar system with energy storage, and panels of a sufficient size, only has to rely on external sources of electricity for a few hours per week. Therefore, advocates of renewable energy think that electricity distribution systems should be less important and easier to control.

Integration into the landscape

Integration into the landscape of turbines.

An obvious drawback of renewable energy is its visual impact on the local environment. Some people hate the aesthetics of wind generators and mention nature conservation when talking about large solar power installations outside of cities^[who?]. However, everyone finds charm in the sight of the "old windmills" which, in their time, were a highly visible example of the available technique.

Others^[who?] are trying to use these technologies in an efficient and aesthetically pleasing way: fixed solar panels can double as noise barriers along highways, roofs are available and could even be completely replaced by solar collectors, amorphous photovoltaic cells that can be used to tint windows and produce energy, etc.^{[citation needed]}

Renewable energy sources today

Hydroelectric power station.

They represent 18,054% of world electricity consumption, 90% of which is of hydraulic origin. The rest is very marginal: biomass 5.5%, geothermal 1.5%, wind 0.5% and solar 0.5%.

About 80% of the energy needs in Western industrial societies are centered around industry, heating, air conditioning in buildings and transport (cars, trains, planes). However, most large-scale applications of renewable energy are concentrated in the production of electricity.

In Spain, renewables were responsible for 19.8% of electricity production. The generation of electricity with renewable energies surpassed that of nuclear origin in 2007.

In the United States, in 2011 renewable energy production surpassed nuclear for the first time, generating 11.73% of the country's total energy. 48% of renewable energy production came from biofuels, and 35% from hydroelectric power plants, the other 16% being wind, geothermal and solar.

Energy production and self-consumption

Greenpeace presented a report in which it maintains that the use of renewable energies to produce 100% of the energy is technically viable and economically acceptable, therefore, according to the environmental organization, the only thing that is missing for Spain to dirty energies are put aside, political will is necessary. To achieve this, two parallel developments are necessary: renewable energy and energy efficiency (elimination of superfluous consumption).

On the other hand, 64% of the managers of the main utilities consider that in the horizon of 2018 there will be clean, affordable and renewable technologies of local generation, which will force the large corporations of the sector to a change of mentality.

The production of green energies is increasing not only due to the development of technology, mainly in the solar field, but also due to clear political commitments, being also one of the sectors that contributes the most to national economic stability. Thus, the Ministry of Industry, Tourism and Commerce of Spain foresees that green energies will reach 83,330 MW, compared to the current 32,512 MW, and can cover 41% of electricity demand in 2030. To reach this quota, it is It plans to previously reach 12% of electricity demand supplied by renewable energies in 2010 and 20% in 2020.

The self-consumption of renewable electricity is contemplated in Royal Decree 1699/2011, of November 18, which regulates the connection to the grid of small-power electricity production facilities.

By countries

• Renewable energy in Latin America
• Renewable energy in the European Union:
  • Renewable energy in Germany
  • Renewable energy in Spain
  • Renewable energy in Argentina

Higher education in renewable energy

Engineering

Renewable Energy Engineering at the National Autonomous University of Mexico in Mexico

Renewable Energy Engineering at the Autonomous University of Baja California in Mexico

Engineering in Renewable Energy Sources at the Autonomous University of Baja California Sur in Mexico

Renewable Energy Engineering at Université de Perpignan Via Domitia in France

Engineering in Sustainable Innovation and Energies at Universidad de Monterrey in Mexico

Postgraduate

CEENER at the Autonomous University of Baja California

Institute of Engineering at the Autonomous University of Baja California

PROMES in Perpignan, France

Institutions that promote Renewable Energies

• IRENA
• ISES - International Solar Energy Association

Continental and national

• LAWEA - Latin American Wind Energy Association
  • ASADES - Asociación Argentina de Energías Renovables y Ambiente
• Agency EUREC, a European association that connects leading research centers and active university departments in the field of renewable energy technology.
  • IDAE, Instituto para la Diversificación y Ahorro de la Energía, Spain.